Landscape factors influencing the distribution of rare submerged plant species: an environmental DNA (eDNA) study

Effective conservation of rare submerged plant species requires understanding not only their habitats but also the surrounding landscape and water quality conditions. However, conventional surveys are often difficult due to the elusive nature of these plants. In this study, we applied environmental DNA (eDNA) analysis to detect species of the genus Najas, several of which are classified as endangered in Japan. We conducted field surveys and eDNA analysis across 158 ponds in western Japan and evaluated the influence of environmental and landscape variables using generalized linear models. Explanatory variables included water quality (pH, dissolved oxygen, electrical conductivity), pond size, shoreline type (soil, forest, concrete), and land use (forest, paddy field, artificial land). Our results showed that Najas presence was positively associated with lower electrical conductivity and longer forested shorelines. These findings suggest that forested pond margins may provide favorable conditions for submerged plants, while eutrophication may reduce habitat suitability. Our study demonstrates that integrating eDNA detection with landscape analysis offers a powerful and efficient approach for monitoring and conserving rare submerged plant species.